System to control the on-off time of a pulse train of variable frequency, particularly the dwell time of ignition signals for an internal combustion engine

In an ignition system for an internal combustion engine having a ignition coil (19),

• a system to control the ON-OFF time of current flow through the primary of the ignition coil, in which the ON time is dependent on a predetermined level of current flowing through said primary of the coil comprising
• means generating a first variable frequency (f1) as a function of engine speed;
• means (10, 13) generating a second frequency (f2) higher than said first frequency;
• a counter (14);
• control transfer switching means (12) connected to apply the first frequency (f1) to the counter (14) to thereby commence a first counting cycle and cause the counter to count at the rate of the first frequency to a predetermined count value (Z1) and, selectively, and when so controlled, connecting and applying the second frequency (f2) to the counter (14) to thereby commence a second counting cycle;
• decode means (15, 16) recognizing when said counter reaches said predetermined count value (Z1) and setting said counter to a predetermined count state (ZERO) and additionally controlling said controlled transfer switching means (12) to apply said second, higher frequency (f2) to the counter to cause the counter to count at the rate of said second, higher frequency;
• current flow responsive means (20, 22, 23) responsive to the level of current flow in the primary of said ignition coil and connected to said counter to inhibit counting of the counter and thus to terminate the second count cycle;
• means (11) generating an ignition trigger signal (A);
• and interrupter switch means (17) connected to said counter (17) closing as a function of the time period after the counter (14) has reached said predetermined count state (ZERO), the ignition trigger signal generating means (11) generating said trigger signal to then interrupt current flow through the primary of the ignition coil, whereby the ON time of said interrupter switch means will be controlled as a function of the speed of the engine and current flow through the ignition coil to provide for closing of said interrupter switch means for a period of time essentially independent of the speed of the engine and will be self adaptive with respect to external operating conditions and self regulating in dependence on the level of current flow through the primary of the ignition coil.